Hydrogen sulfide can be removed from an H.sub.2 S-containing feed gas by the Claus process for producing elemental sulfur, wherein the feed gas is partially burnt with oxygen-containing gas in a thermal Claus process plant having at least one combustion chamber, wherein temperatures in the range of 850.degree. to 1350.degree. C. are maintained. The resulting process gas is passed through a catalytic Claus process plant (Claus catalysis plant), from which sulfur is withdrawn. The exhaust gas from the Claus catalysis plant is supplied to a desulfurizing plant in which the sulfur compounds contained in the exhaust gas from the desulfurizing plant are converted to SO.sub.2 by a thermal aftertreatment, and an SO.sub.2 -containing exhaust gas is produced. Small quantities of other sulfur compounds, such as COS, CS.sub.2 and methyl mercaptans, are also removed by the process.
That process and equipment for carrying out the process have been described in detail in Ullmanns Enzyklopadie der Technischen Chemie, 4th edition (1982), vol. 21, pp 8 to 26. In the thermal Claus process plant the H.sub.2 S-containing feed gas is burnt with air or oxygen-enriched air to produce a mixture of H.sub.2 S and SO.sub.2 ; a molar ratio of 2:1 of the two components is desired in that step.
In the Claus catalysis plant, the reaction is 2H.sub.2 S+SO.sub.2 =3S+2H.sub.2 O to form elemental sulfur and water. Al.sub.2 O.sub.3 catalysts having surface areas of 200 to 300 m.sup.2 /g may be used for that purpose.
The desulfurizing plant may be operated in accordance with any of a number of processes, in which the sulfur compounds are removed by adsorption and/or absorption. The thermal aftertreatment is generally an afterburning, by which all sulfur compounds are converted to sulfur dioxide.
It frequently is necessary to provide a technique which will ensure a satisfactory operation of the units of the plant even if the rate of feed gas varies greatly. It is also desirable to avoid problems which might arise as a result of a temperature drop below the dew point temperature and the solidification temperature of sulfur.